Performance of the diamond-based beam-loss monitor system of Belle II

At a Glance

Metadata	Details
Publication Date	2021-02-17
Journal	Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
Authors	S. Bacher, G. Bassi, L. Bosisio, G. Cautero, P. Cristaudo
Institutions	University of Pisa, Elettra-Sincrotrone Trieste S.C.p.A.
Citations	28
Analysis	Full AI Review Included

Diamond-Based Beam-Loss Monitoring for SuperKEKB: 6CCVD Technical Analysis

This document analyzes the performance requirements and material specifications detailed in the research paper “Performance of the diamond-based beam-loss monitor system of Belle II” and outlines how 6CCVD’s advanced MPCVD diamond solutions can meet and exceed these technical demands for high-energy physics and accelerator applications.

Executive Summary

The successful deployment of single-crystal diamond (SCD) sensors for beam-loss monitoring (BLM) and accelerator interlocks at the SuperKEKB collider validates the critical role of high-purity CVD diamond in extreme radiation environments.

Proven Application: SCD sensors reliably monitor dose rates (up to 140 krad/s) and protect sensitive inner detectors (Belle II VXD) and superconducting magnets (QCS) from destructive beam losses.
Radiation Hardness: The SCD detectors sustained total integrated doses up to 960 krad (0.96 MGy) during Phase 3 operations without significant performance degradation.
Ultra-Fast Response: The system achieved a critical time resolution of 2.5 µs for fast abort requests, essential for matching the 10 µs revolution time of the SuperKEKB rings.
Material Specification: Electronic grade SCD (4.5 x 4.5 x 0.5 mm³) with custom Ti/Pt/Au metalization was utilized, demonstrating high charge collection efficiency (G ≈ 1).
Future Requirements (Sales Opportunity): The research identifies a need for materials and electronics with a wider dynamic range to handle future luminosity increases and prevent saturation during high-current injection events.
6CCVD Advantage: 6CCVD specializes in custom SCD wafers, precise thickness control (0.1 µm to 500 µm), and internal metalization capabilities (Ti/Pt/Au stacks), directly addressing the needs for replication and future system upgrades.

Technical Specifications

The following hard data points were extracted from the analysis of the Belle II diamond BLM system:

Parameter	Value	Unit	Context
Sensor Material	Single-Crystal Diamond (sCVD)	N/A	Electronic Grade
Sensor Dimensions	4.5 x 4.5 x 0.5	mm³	Standard size used
Electrode Stack	Ti + Pt + Au (100 + 120 + 250)	nm	Deposited on both faces
Operating Bias Voltage	100	V	Chosen for full charge-collection efficiency
Dose Rate Conversion Factor (F)	34.9	(mrad/s)/nA	Typical sensitivity (assuming G=1)
Maximum Dose Rate Range	140	krad/s	Range 2 setting (4.5 mA current range)
Minimum Dose Rate Sensitivity	1.1	rad/s	Range 0 setting (36 nA current range)
Fast Abort Time Resolution	2.5	µs	Updated DCU firmware cycle time
SuperKEKB Revolution Time	10	µs	Critical time scale for beam aborts
Lowest Rms Noise (10 Hz data)	0.8	pA	Range 0 (36 nA current range)
Maximum Integrated Dose (Phase 3)	960	krad	Recorded by QCS_FW_225 detector

Key Methodologies

The diamond sensors were prepared and deployed using the following critical steps:

Material Selection: Electronic grade Single-Crystal Diamond (sCVD) was chosen for its radiation hardness and high charge carrier mobility, ensuring a temperature-independent response.
Detector Dimensions: Standard 4.5 x 4.5 x 0.5 mm³ SCD plates were used, balancing active volume with compact size for installation near the interaction point (IP).
Metalization Process: Two electrodes consisting of a Ti + Pt + Au stack (100 nm Ti, 120 nm Pt, 250 nm Au) were deposited on both faces to ensure robust electrical contact and stability.
Packaging: Sensors were mounted on Rogers printed circuit boards for mechanical support and electrical screening, connected via miniature coaxial cables (conductive glue and gold wire ball bonding).
Calibration: Detectors were characterized using dark current measurements, stability tests, and transport property analysis using ²⁴¹Am (alpha) and ⁹⁰Sr (beta) radioactive sources to determine the current-to-dose-rate calibration factor k.
Readout Electronics: Custom Diamond Control Units (DCUs) utilized 16-bit ADCs sampling at 50 Msamples/s, processed by FPGAs to provide three distinct current measurement ranges (36 nA to 4.5 mA) and deliver fast abort requests based on moving sums updated every 2.5 µs.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity MPCVD diamond required to replicate, enhance, and extend the capabilities of the Belle II beam-loss monitoring system.

Applicable Materials

The high-performance requirements (G ≈ 1, low noise, high radiation tolerance) necessitate the use of the highest purity material.

Optical Grade Single Crystal Diamond (SCD): Recommended for replicating the electronic grade sCVD sensors used in this study. Our SCD offers superior purity and crystalline quality, ensuring maximum charge collection efficiency (CCE) and minimal trapping/detrapping effects, crucial for accurate dose rate measurements.
Custom Thickness SCD: The paper used 500 µm thick sensors. 6CCVD can supply SCD wafers from 0.1 µm up to 500 µm. Thinner SCD layers can be engineered to reduce detector capacitance, potentially enabling even faster signal rise times and improving the dynamic range of the readout electronics, addressing the limitations noted in the paper’s outlook.

Customization Potential

6CCVD’s in-house fabrication capabilities directly match the specific requirements of high-energy physics detector construction.

Requirement from Paper	6CCVD Capability	Technical Advantage
Custom Dimensions	Plates/wafers up to 125 mm (PCD) and custom SCD sizes available.	We can supply the exact 4.5 x 4.5 mm² dimensions or larger SCD plates for array fabrication.
Metalization Stack	Internal capability for Ti, Pt, and Au deposition.	We can precisely replicate the required Ti/Pt/Au (100/120/250 nm) electrode stack used for stable ohmic contacts. We also offer Pd, W, and Cu for alternative designs.
Surface Finish	Polishing to Ra < 1 nm (SCD).	Ultra-low roughness is critical for uniform electrode deposition and minimizing surface leakage currents, enhancing detector stability and noise performance (0.8 pA noise floor).
Shipping & Logistics	Global shipping (DDU default, DDP available).	Reliable delivery of sensitive, high-value diamond components worldwide to accelerator laboratories (e.g., KEK, INFN).

Engineering Support

The research highlights the ongoing challenge of optimizing dynamic range and time resolution for future high-luminosity operations.

Dynamic Range Optimization: 6CCVD’s in-house PhD team can assist engineers in selecting optimal SCD thickness and doping levels to tailor detector response. For instance, exploring thinner SCD or potentially lightly Boron-Doped Diamond (BDD) layers could help manage the high current spikes (up to 4.5 mA) observed during injection, thereby expanding the effective dynamic range without saturation.
Accelerator Physics Consultation: We offer expert material consultation for similar Beam-Loss Monitoring (BLM), Beam Condition Monitoring (BCM), and High-Energy Particle Tracking projects, leveraging our deep understanding of diamond charge transport properties (G factor).

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.nima.2021.165157

References

2013 - Accelerator design at SuperKEKB
2018 - Detectors for extreme luminosity: Belle II [Crossref]
2017 - Beam loss and abort diagnostics during SuperKEKB phase-I operation
2019 - First measurements of beam backgrounds at SuperKEKB [Crossref]
2020 - Highlights from superkekb commissioning for early stage of nano-beam scheme and crab waist scheme
2013 - Progress in KEKB beam instrumentation systems
2004 - Radiation hardness and monitoring of the BABAR vertex tracker [Crossref]
2005 - Radiation monitoring with CVD diamonds in babar [Crossref]